Semiconductor device

ABSTRACT

A semiconductor device includes: a semiconductor substrate having two types of active regions that are a PMOS region and an NMOS region separated from each other in plan view by a PN separation film; and a dual-gate electrode extending linearly across the PMOS region, the PN separation film and the NMOS region collectively on an upper side of the semiconductor substrate. The dual-gate electrode includes a P-type portion, an N-type portion and a PN junction positioned therebetween. The PN junction includes a silicide region. The silicide region is apart from both the PMOS region and the NMOS region and formed within the area of the PN separation film in plan view.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device. More particularly, the present invention relates to a semiconductor device with a complementary metal oxide semiconductor (CMOS) transistor.

[0003] 2. Description of the Background Art

[0004] A CMOS transistor is a transistor where an NMOS transistor and a PMOS transistor are paired. A dual-gate electrode is a single continuous gate electrode used as a common gate electrode by the NMOS and PMOS transistors. The dual-gate electrode in an area for configuring the NMOS transistor is formed of N+ polycrystal silicon while the dual-gate electrode in an area for configuring the PMOS transistor is formed of P+ polycrystal silicon.

[0005] Conventionally, for a semiconductor device with the CMOS transistor, particularly for a semiconductor device with the CMOS transistor adopting the dual-gate electrode, only the entire region of the active region, the dual-gate electrode and the interconnection is selectively silicided to connect the N+ polycrystal silicon portion and the P+ polycrystal silicon portion in the dual-gate electrode with low resistivity, by using a technique of siliciding a high-melting-point metal in a self-aligned manner. An example is disclosed in Japanese Patent Laying-Open No. 59-107540.

[0006] Since the entire region of the active region, the dual-gate electrode and the interconnection is conventionally silicided, an insulating film of identical shape with the dual-gate electrode cannot be formed such that it covers an upper side of the dual-gate electrode after silicidation. Accordingly, such an insulating film cannot be used as a stopper film to form a contact hole in a self-aligned manner.

[0007] Additionally, when the entire active region is silicided with the technique of siliciding a high-melting-point metal, a problem such as abnormal silicidation often causes electrical leakage between the active region and the well. Therefore, silicidation of the active region is not desirable.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide a semiconductor device having a CMOS transistor device with a dual-gate electrode, in which a contact hole can be formed in a self-aligned manner and electrical leakage between the active region and the well can be eliminated.

[0009] In order to achieve the object described above, a semiconductor device in accordance with the present invention includes: a semiconductor substrate having two types of active regions that are a PMOS region and an NMOS region separated from each other in plan view by a PN separation film, and a dual-gate electrode extending linearly across the PMOS region, the PN separation film and the NMOS region collectively on an upper side of the semiconductor substrate. The dual-gate electrode includes: a P-type portion positioned on the PMOS region; an N-type portion positioned on the NMOS region; and a PN junction positioned between the P-type portion and the N-type portion. The PN junction includes a silicide region having been subjected to silicidation. The silicide region is apart from both the PMOS region and the NMOS region and formed within the area of the PN separation film.

[0010] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a plan view of a semiconductor device in a first embodiment in accordance with the present invention.

[0012]FIG. 2 is a cross section taken along a line II-II in FIG. 1.

[0013]FIG. 3 is a cross section taken along a line III-III in FIG. 1.

[0014]FIG. 4 is a vertical cross section in a first step of a method of manufacturing a semiconductor device in the first embodiment in accordance with the present invention.

[0015]FIG. 5 is a transverse cross section in the first step of the method of manufacturing a semiconductor device in the first embodiment in accordance with the present invention.

[0016]FIG. 6 is a vertical cross section in a second step of the method of manufacturing a semiconductor device in the first embodiment in accordance with the present invention.

[0017]FIG. 7 is a transverse cross section in the second step of the method of manufacturing a semiconductor device in the first embodiment in accordance with the present invention.

[0018]FIG. 8 is a vertical cross section in the third step of the method of manufacturing a semiconductor device in the first embodiment in accordance with the present invention.

[0019]FIG. 9 is a transverse cross section in the third step of the method of manufacturing a semiconductor device in the first embodiment in accordance with the present invention.

[0020]FIG. 10 is a graph showing the junction leakage characteristic of a semiconductor device in the first embodiment in accordance with the present invention.

[0021]FIG. 11 is a graph showing the junction leakage characteristic of a conventional semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] First Embodiment

[0023] Referring to FIGS. 1 to 3, a semiconductor device of a first embodiment in accordance with the present invention will be described. In FIG. 1, for convenience of description, a silicidation prevention film 8 and a gate-etching mask 5 which cover an upper side of a dual-gate electrode 4 are not shown in order that dual-gate electrode 4 can directly be seen. FIG. 2 is a cross section taken along a line II-II in FIG. 1. FIG. 3 is a cross section taken along a line III-III in FIG. 1. The semiconductor device includes a semiconductor substrate 1 and dual-gate electrode 4 as shown in FIGS. 2 and 3. The surface of semiconductor substrate 1 is partially covered with a separation insulating film 2. Semiconductor substrate 1 has two types of active regions 20, i.e., a PMOS region and an NMOS region that are separated from each other in plan view, namely as seen from the above, by a PN separation film 3 which is a part of separation insulating film 2.

[0024] Dual-gate electrode 4 extends linearly across the PMOS region, PN separation film 3 and the NMOS region collectively on an upper side of semiconductor substrate 1. Dual-gate electrode 4 includes a P-type polycrystal silicon portion 4 a which is a P-type portion positioned on the PMOS region, and an N-type polycrystal silicon portion 4 b which is an N-type portion positioned on the NMOS region. Dual-gate electrode 4 further includes a PN junction positioned between P-type polycrystal silicon portion 4 a and N-type polycrystal silicon portion 4 b. The PN junction includes a silicide region 9. The silicide region is a silicided region. Silicide region 9 is positioned apart from the PMOS region and the NMOS region and within the area of PN separation film 3 in plan view.

[0025]FIG. 1 shows contacts 12 by symbols. Contacts 12 are provided for ensuring electrical connection for active regions 20, and are formed in active regions 20 such that dual-gate electrode 4 is positioned between them in plan view. Contacts 12 are positioned to overlap dual-gate electrode 4 in plan view.

[0026] As shown in FIG. 2, dual-gate electrode 4 is covered with a sidewall insulating film 6 and then with a silicidation prevention film 8 thereon, except for the PN junction. At the PN junction, in the absence of sidewall insulating film 6 and silicidation prevention film 8, a salicide opening 7 is formed. Silicide region 9 is exposed inside salicide opening 7. As shown in FIG. 3, silicidation prevention film 8 is not formed in an area where contacts 12 overlap dual-gate electrode 4. However, dual-gate electrode 4 is covered with sidewall insulating film 6 to ensure electrical insulation from contacts 12.

[0027] The entire region of dual-gate electrode 4 is substantially covered with silicidation prevention film 8 except for silicide region 9. With this configuration, silicidation can conveniently be performed in a self-aligned manner as described below.

[0028] Function and Effect

[0029] The semiconductor device in this embodiment has a CMOS transistor device with dual-gate electrode 4. Silicide region 9 of dual-gate electrode 4 is formed at the PN junction only while the other portions thereof are covered with sidewall insulating film 6. Consequently, a contact hole can be formed in a self-aligned manner; actually, the semiconductor device has contacts 12 formed in a self-aligned manner. In this semiconductor device, silicidation of the entire active regions 20 is unnecessary, which can eliminate electrical leakage between the active regions and the well.

[0030] In particular, in this semiconductor device, silicide region 9 is positioned apart from both the PMOS region and the NMOS region and within the area of PN separation film 3 in plan view. Such configuration is preferred to prevent electrical leakage between silicide region 9 and active regions 20.

[0031] In this semiconductor device, contacts 12 are positioned to overlap dual-gate electrode 4 in plan view. If contacts 12 are positioned apart from dual-gate electrode 4, however, the effect of the present invention can be exhibited to a certain degree. However, when the present invention is applied, contacts 12 can be formed to overlap dual-gate electrode 4. Since this can reduce an area occupied by the transistor, such overlapping configuration is preferred. According to an estimation, as compared with the conventional configuration where the contacts are required to be positioned apart from the dual-gate electrode, it has been found that the configuration of the embodiment of the present invention can reduce the area occupied by the transistor by approximately 30% since the contacts are positioned to overlap the gate electrode.

[0032] Additionally, contacts 12 are positioned to avoid silicide region 9 in plan view. In other words, contacts 12 are positioned not to overlap silicide region 9. Such configuration is preferred to prevent electrical leakage between silicide region 9 and contacts 12. Contacts 12 are also positioned to avoid PN separation film 3 in plan view. Such configuration is preferred to efficiently ensure electrical connection of active regions 20 by contacts 12.

[0033] Silicidation prevention film 8 preferably includes a silicon nitride film because it is easily formed and formed of an appropriate material for preventing silicidation of the electrode portion.

[0034] Referring to FIGS. 4 to 8, FIG. 2 and FIG. 3, a method of manufacturing a semiconductor device according to this embodiment will be described. FIGS. 4, 6 and 8 are cross sections seen in the same direction as that of FIG. 2. FIGS. 5, 7 and 9 are cross sections seen in the same direction as that of FIG. 3.

[0035] As shown in FIGS. 4 and 5, a gate oxide film 13 is formed on an upper surface of semiconductor substrate 1. A polycrystal silicon film is then formed thereon as a material to form dual-gate electrode 4. The polycrystal silicon film is formed by a known technique such that N-type polycrystal silicon is formed in the NMOS region while P-type polycrystal silicon is formed in the PMOS region. An insulating film including a silicon nitride film is then formed to cover an upper side of the polycrystal silicon film. The insulating film is patterned to serve as gate-etching mask 5. Gate-etching mask 5 is used as an etching mask to pattern the polycrystal silicon film. As a result, a configuration of dual-gate electrode 4 is obtained as shown in FIGS. 4 and 5.

[0036] As shown in FIGS. 6 and 7, sidewall insulating film 6 is formed to cover a side of dual-gate electrode 4 covered with gate-etching mask 5.

[0037] As shown in FIGS. 8 and 9, silicidation prevention film 8 is formed to cover the upper side of the entire region of dual-gate electrode 4. Silicidation prevention film 8 is preferably formed of a silicon nitride film. Silicidation prevention film 8 and gate-etching mask 5 are removed by etching, for example, such that only the PN junction is exposed. As a result, salicide opening 7 is formed as shown in FIG. 8. Silicidation is then performed such that only the portion exposed at salicide opening 7 in dual-gate electrode 4 is silicided. Since the entire region of dual-gate electrode 4 is substantially covered with silicidation prevention film 8 except for the region to be silicided, silicidation can be performed in a self-aligned manner. As a result, silicide region 9 is formed as shown in FIG. 8.

[0038] As shown in FIGS. 2 and 3, an interlayer insulating film 10 is deposited thereon. Contact holes are formed in a self-aligned manner such that they overlap dual-gate electrode 4 in plan view with respect to interlayer insulating film 10. In forming the contact holes, silicidation prevention film 8 is used as a stopper film. The contact holes reach the surface of active regions 20 only in the area where they directly overlap active regions 20 in plan view. A conductive material fills the contact holes to form contacts 12. As a result, the semiconductor device shown in FIGS. 1 to 3 can be obtained.

[0039] Some conventional configurations having contacts overlapping a silicide region show a junction leakage current which varies as shown in FIG. 11. In contrast, a configuration to which the present invention is applied to have contacts without overlapping a silicide region shows a junction leakage current which varies to a smaller degree as shown in FIG. 10, and thus the junction leakage current can be controlled.

[0040] In accordance with the present invention, in a CMOS transistor device with a dual-gate electrode, contact holes can be formed in a self-aligned manner, and electrical leakage between the active regions and the well can be eliminated.

[0041] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

What is claimed is:
 1. A semiconductor device comprising: a semiconductor substrate having two types of active regions that are a PMOS region and an NMOS region separated from each other in plan view by a PN separation film; and a dual-gate electrode extending linearly across said PMOS region, said PN separation film and said NMOS region collectively on an upper side of said semiconductor substrate, said dual-gate electrode including a P-type portion positioned on said PMOS region, an N-type portion positioned on said NMOS region and a PN junction positioned between said P-type portion and said N-type portion, and said PN junction including a silicide region having been subjected to silicidation, and said silicide region is apart from both said PMOS region and said NMOS region and formed within an area of said PN separation film in plan view.
 2. The semiconductor device according to claim 1, wherein said dual-gate electrode is substantially covered with a silicidation prevention film except for said silicide region.
 3. The semiconductor device according to claim 2, wherein said silicidation prevention film includes a silicon nitride film.
 4. The semiconductor device according to claim 1 further comprising a contact positioned on said active regions such that said contact overlaps said dual-gate electrode in plan view.
 5. The semiconductor device according to claim 4, wherein said contact is positioned to avoid said silicide region in plan view.
 6. The semiconductor device according to claim 4, wherein said contact is positioned to avoid said PN separation film in plan view. 